1. Field of the Invention
This invention relates generally to medical imaging, and more particularly concerns a method for automatic scan prescription for tomographic imaging, such as magnetic resonance imaging (MRI), computer tomography (CT), and other tomographic imaging techniques. More specifically, the invention relates to methods to automatically determine scan orientations and locations for tomographic imaging scans.
2. Description of Related Art
In computerized tomography (CT), an image of a section or slice of a region of interest of a patient is typically obtained from a large number of narrow X-ray beam projections, at multiple angles through the slice, for providing multiplanar imaging of the patient. Modern CT scanners commonly provide a detector array mounted opposite the X-ray source, or a ring of detectors completely surrounding the region of interest of the patient, that sequentially detect the X-ray source as it is rotated around the patient. From the many individual measurements from the detectors, from either a single slice, a series of slices, or a helical scan, a computer is commonly used to fill in image data for a matrix of pixels with digital values representing the X-ray intensity measured during the scans.
While the human eye can only differentiate a limited number of shades of gray, computerized digital image data with much finer gradations can be utilized for identification and recognition of structures. One known X-ray computed tomography system is capable of specifying a slice plane corresponding to a desired tomographic image from a data base of helical or multiple scans of a subject. A scanogram of the subject is displayed, on which a cursor is controlled to identify the desired slice planes corresponding to the desired tomographic images to be reconstructed. The desired tomographic images are reconstructed for the desired slice planes indicated by the cursor by using an appropriate portion of the projection data, corresponding to the desired slice planes indicated by the cursor.
Another computed tomography system is known that includes an image reconstruction data generator for generating image reconstruction data for a desired slice plane of an object in accordance with projection data obtained at a plurality of rotation positions of a radiation source. The system also includes an image reconstructor for obtaining tomographic image data of the object for the desired slice plane, according to the image reconstruction data.
While CT can-be more advantageous for scanning bone structures than magnetic resonance imaging (MRI), MRI scanning is advantageous for imaging soft tissue structures, and can be used for multiplanar imaging of a patient. One such MRI imaging system is known, for example, for determining an MRI image plane, such as for imaging the head of a human being, in which the location of the plane of imaging, and its orientation are determined by computer analysis of the distance between manually selected points of the image, and the ratios of the distances between them.
Despite numerous advances in image processing of scanned images, tomographic scanning of patients for medical purposes is still generally performed according to manual prescriptions by specially trained medical technologists. In conventional tomographic imaging, prescription of scanning orientations, locations and angles requires a considerable amount of detailed input and control by the medical technologist. A typical scanning session begins with the acquisition of a "localizer" or "pilot" scan which provides an overview of major anatomical features, such as size and position, of a patient's body or body part to be scanned. Following the localizer scan, several additional scans are usually performed to gain more detailed information about the portion of the patient of interest. For each additional scan, the medical technologist uses the localizer scan or previous scans to manually define the boundaries and the orientation of the spatial volume to be scanned, such that it fully includes the region of interest.
Such conventional procedures for manually prescribing scan locations are relatively time consuming. As a result, human operators of tomographic imaging devices spend a considerable percentage of their time on this task, and are commonly unable to finish the manual prescription for a next scan before a current scan is finished, resulting in inefficient use of valuable scan time.
Currently, a scan technologist piloting the scanner equipment attempts to manually define scanning parameters that are appropriate for each individual patient. However, manual scan prescription by human operators is often crude, as the operators usually are not able to fully explore all degrees of freedom that need to be optimized in order to obtain the best possible scan. For example, many scanning parameters such as rotations of the tomographic imaging plane are kept at their default value. One of the consequences of this limited use of the available scanning parameters is an inaccurate, non-standardized prescription, yielding scan orientations that vary from one individual to another. With medical scans, such a variability in the scans makes interpretation of the scanned images by radiologists more difficult, and .may ultimately lead to reduced quality of radiologic readings.
Another consequence of the variability in the scan orientations is poor reproducibility for repeat scans, i.e., very different images are usually obtained when the same subject is scanned in different sessions, for example for follow-up of medical conditions, making direct comparison of scans from different sessions difficult.
It can thus be readily appreciated that there is a need for a method and system for automatic prescription of tomographic scans, according to standardized protocols, that minimizes the involvement of a human operator, and that permits reproducible multiple scanning of the same object or organ at different points in time. Such a method would be advantageous for providing accurate and reproducible prescriptions for studies that depend on one or more previous prescriptions. It would also be desirable to provide a method for automatic definition of specific regions of interest within a larger object or organ of interest in the tomographic imaging device for use with scanning methods to obtain information from the specific regions of interest, such as for localized magnetic resonance spectroscopy, for example, to obtain chemical information from within a well defined region of interest.
The present invention meets these needs.